Image reading apparatus and image reading method

ABSTRACT

An image reading apparatus having a color line sensor and a monochromatic line sensor starts to read on the basis of the color reading start position when reading the image of a document in color and starts to read on the basis of the monochromatic reading start position when reading the image of a document in monochrome.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom prior Japanese Patent Application No. 2003-056324, filed Mar. 3,2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003] This invention relates to an image reading apparatus and an imagereading method which scan the reading face of a document optically andconvert the scanned data into color image data or monochromatic imagedata.

[0004] 2. Description of the Related Art

[0005] In a conventional image reading apparatus (or a color imagereading apparatus) which reads images on a document in color, the entiredocument is scanned optically by moving the carriage and the colorimages are read by the color CCD sensor. The conventional color imagereading apparatus uses a 3-line CCD sensor as a color CCD sensor. The3-line CCD sensor is composed of the following three line CCD sensors: afirst line CCD sensor that outputs a red component (R signal), a secondline CCD sensor that outputs a green component (G signal), and a thirdline CCD sensor that outputs a blue component (B signal). In an imagereading apparatus with three line CCD sensors, when a monochromaticimage is read, a monochromatic image is created on the basis of thesignals (RGB signals) outputted from the three line sensors.

[0006] In the conventional image reading apparatus, the output of eachof the three line CCD sensors constituting the 3-line CCD sensor is notalways uniform. This nonuniformity results from variations in thesensitivity of a pixel unit in each line CCD sensor and a decrease inthe amount of light around the lens caused by the light distributioncharacteristic of the exposure lamp that illuminates the document andthe characteristic of the lens. Thus, in the conventional image readingapparatus, a reference plate (shading correction plate) acting as awhite reference is read by the 3-line CCD sensor. On the basis of theresult of the reading, the output signal from the 3-line CCD sensor iscorrected (or the shading is corrected).

[0007] Therefore, in the image reading apparatus with the 3-line CCDsensor, the white reference plate is always read in the same readingposition. This is because the image reading apparatus with the 3-lineCCD sensor reads not only color images but also monochromatic imageswith the three line CCD sensors. Consequently, the conventional imagereading apparatus with the three-line CCD sensor reads the shadingcorrection plate in the fixed reading position, regardless of whetherthe image of the document is read in color or in monochrome, and makes ashading correction of the output signal from each line sensor.

BRIEF SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide an imagereading apparatus and an image reading method which are capable of notonly reading color images and monochromatic images efficiently but alsomaking a shading correction effective and the image reading apparatusmore compact and stable by making the width of the reference platesmaller.

[0009] According to an aspect of the present invention, there isprovided an image reading apparatus which reads images on the readingface of a document in color or in monochrome, the image readingapparatus comprising: a line sensor which includes a color line sensorfor reading a color image and a monochromatic line sensor for reading amonochromatic image different from the color line sensor; a scanningsection on which an optical system for directing light from the readingface of the document to the line sensor is provided; a driving mechanismwhich moves the scanning section in a feed direction with respect to thereading face of the document; a reference plate which is provided infront of the leading edge of the reading face of the document in thefeed direction in which the scanning section is moved by the drivingmechanism; and a control section which, when the reading face of thedocument is read in color, starts to read the reference plate with thecolor line sensor at the time that the scanning section moved in thefeed direction by the driving mechanism reaches a color reading startposition for the reference plate, thereby reading the reference platewith the color line sensor, and which, when the reading face of thedocument is read in monochrome, starts to read the reference plate withthe monochromatic line sensor at the time that the scanning sectionmoved in the feed direction by the driving mechanism reaches amonochromatic reading start position for the reference plate, therebyreading the reference plate with the monochromatic line sensor.

[0010] According to another aspect of the present invention, there isprovide an image reading method used in an image reading apparatus whichcomprises a line sensor which includes a color line sensor for reading acolor image and a monochromatic line sensor for reading a monochromaticimage different from the color line sensor, a scanning section on whichan optical system for directing light from the reading face of thedocument to the line sensor is provided, a driving mechanism which movesthe scanning section in a feed direction with respect to the readingface of the document, and a reference plate which is provided in frontof the leading edge of the reading face of the document in the feeddirection in which the scanning section is moved by the drivingmechanism, the image reading method comprising: when the reading face ofthe document is read in color, starting to read the reference plate withthe color line sensor at the time that the scanning section moved in thefeed direction by the driving mechanism reaches a color reading startposition for the reference plate and thereby reading the reference platewith the color line sensor; and when the reading face of the document isread in monochrome, starting to read the reference plate with themonochromatic line sensor at the time that the scanning section moved inthe feed direction by the driving mechanism reaches a monochromaticreading start position for the reference plate and thereby reading thereference plate with the monochromatic line sensor.

[0011] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0012] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate an embodiment of theinvention, and together with the general description given above and thedetailed description of the embodiment given below, serve to explain theprinciples of the invention.

[0013]FIG. 1 shows the configuration of a 4-line CCD sensor provided inan image reading apparatus according to an embodiment of the presentinvention;

[0014]FIG. 2 schematically shows the configuration of the image readingapparatus according to the embodiment;

[0015]FIG. 3 is a block diagram of the control system of the imagereading apparatus;

[0016]FIG. 4 is a flowchart to help explain the operation of the entireimage reading apparatus roughly;

[0017]FIG. 5 is a diagram to help explain the operation in a case wherethe four line sensors read a shading correction plate in turn;

[0018]FIG. 6 is a diagram to help explain a shading correction platereading operation in a first reading method;

[0019]FIG. 7 is a diagram to help explain a shading correction platereading operation in a second reading method;

[0020]FIG. 8 is a diagram to help explain a shading correction platereading operation in a third reading method;

[0021]FIG. 9 is a diagram to help explain a shading correction platereading operation in a fourth reading method;

[0022]FIG. 10 is a diagram to help explain a shading correction platereading operation in a fifth reading method; and

[0023]FIG. 11 is a diagram to help explain a shading correction platereading operation in a sixth reading method.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, referring to the accompanying drawings, anembodiment of the present invention will be explained.

[0025]FIG. 1 shows a configuration diagram of a 4-line CCD sensor 1provided in an image reading apparatus according to an embodiment of thepresent invention.

[0026] As shown in FIG. 1, the 4-line CCD sensor 1 comprises a red linesensor R that converts the red component of the incident lightphotoelectrically into an R signal representing the intensity of red, agreen line sensor G that converts the green component of the incidentlight photoelectrically into a G signal representing the intensity ofgreen, a blue line sensor B that converts the blue component of theincident light photoelectrically into a B signal representing theintensity of blue, and a black-and-white line sensor BW that convertsthe black and white components of the incident light photoelectricallyinto a BW signal representing the intensity of black and white.

[0027] In the 4-line CCD sensor 1, the red line sensor R, green linesensor G, and blue line sensor B constitute a color line sensor thatreads images in color. The black-and-white line sensor BW constitutes amonochromatic line sensor that reads images in monochrome.

[0028] The red line sensor R is composed of a CCD line sensor with a redfilter. Therefore, the red line sensor R can take in only the redcomponent of the incident light and output an R signal.

[0029] The green line sensor G is composed of a CCD line sensor with agreen filter. Therefore, the green line sensor G can take in only thegreen component of the incident light and output and a G signal.

[0030] The blue line sensor B is composed of a CCD line sensor with ablue filter. Therefore, the blue line sensor B can take in only the bluecomponent of the incident light and output and a B signal.

[0031] In the 4-line CCD sensor 1, the line sensors R, G, B, BW arearranged in parallel at specific intervals. In an example of FIG. 1, theline sensors are arranged in this order: R, G, B, BW. Each of thespacing between the red line sensor R and the green line sensor G andthe spacing between the green line sensor G and the blue line sensor Bis equivalent to eight lines. The spacing between the blue line sensor Band the black-and-white line sensor BW is equivalent to 12 lines.

[0032] Specifically, as the color line sensors, the red line sensor R,green line sensor G, and blue line sensor B are arranged in parallel atintervals of eight lines. As the monochromatic line sensor, theblack-and-white sensor BW is arranged in parallel with the blue linesensor B acting as a color line sensor, spaced 12 lines apart. One linecontains, for example, 7450 pixels. One pixel has a size of 4.7 μm×4.7μm.

[0033] Next, the configuration of the image reading apparatus providedwith the 4-line CCD sensor will be explained.

[0034]FIG. 2 shows a configuration of the image reading apparatusaccording to the embodiment of the present invention.

[0035] As shown in FIG. 2, the image reading apparatus 10 comprises ashading correction plate 11, a document table 12, an exposure lamp 14, areflector 15, a first mirror 16, a first carriage 18, a second carriage20, a second mirror 22, a third mirror 24, an image forming lens 26, adriving motor 30, and a control unit (control board) 32.

[0036] The shading correction plate 11 is a reference plate for making ashading correction of the output signal of each line sensor of the4-line CCD sensor on a pixel basis. The shading correction plate 11shows a white reference. Specially, in the shading correction, theoutput data in pixels from each line sensor of the 4-line CCD sensor 1is corrected on the basis of the data read from the shading correctionplate 11.

[0037] The width in the feed direction of the shading correction plate11 is determined by the spacing between the individual line sensors, thenumber of reads (the number of reading lines), the reading magnification(the travel speed of the first carriage), and others. In theconfiguration of FIG. 2, the shading correction plate 11 is providedjust in front of the document table 12 in the direction in which animage is read with the first carriage 18 (or in the feed direction).

[0038] The shading correction plate 11 has to be read before thedocument image is read. It also has to be read in a state where thefirst carriage 18 is moving stably. For this reason, the shadingcorrection plate 11 has to be provided in front of the document imagereading area (or in front of the leading edge of the document) andbehind the position where the travel speed of the first carriage 18started from a specific standby position becomes stable.

[0039] Since the above restriction is put on the installation locationof the shading correction plate 11 in the image reading apparatus 10, itis desirable that the width in the feed direction of the shadingcorrection plate 11 should be as narrow as possible. In addition, it isdesirable that the shading correction plate 11 should be readefficiently.

[0040] The document table 12 is composed of a colorless, transparentmember, such as glass, which permits light to pass through. The documenttable 12 is provided with a document cover (not shown). The document onthe document table 12 is pressed against the glass surface of thedocument table 12 by the document cover (not shown).

[0041] The exposure lamp 14 functions as a light source to eliminate theshading correction plate 11 and the document D put on the document table12. The reflector 15 reflects a part of the light from the exposure lamp14 and illuminates the document D. The first mirror 16 deflects thereflected light from the shading correction plate 11 or the document Din a specific direction.

[0042] The first carriage 18 is provided with the exposure lamp 14,reflector 15, first mirror 16, and others. The first carriage 18 isprovided under the document table 12 so as to be movable in parallelwith the document table 12. The first carriage 18 is moved back andforth under the document table 12 by a driving motor 30 connected to thecarriage 18 via a toothed belt (not shown) and others. The driving motor30 is composed of a stepping motor driven by a driving pulse signal orthe like from the control unit 32.

[0043] Furthermore, under the document table 12, the second carriage 20is provided so as to be movable in parallel with the document table 12.On the second carriage 20, the second mirror 22 and third mirror 24which deflect sequentially the reflected light from the document Ddeflected by the first mirror 16 are so provided that they cross eachother at right angles. The driving force of the driving motor 30 isimparted to the second carriage 20 by the toothed belt and others whichdrive the first carriage 18, with the result that the second carriage 20is moved according to the movement of the first carriage 18. The secondcarriage 20 is moved in parallel with the document table 12 at a speedhalf of the speed of the first carriage 18.

[0044] In addition, under the document table 12, there are provided theimage forming lens 26 which converges the reflected light from the thirdmirror 24 mounted on the second carriage 20 and the 4-line CCD sensor 1which receives the reflected light converged by the image forming lens26 and converts it photo-electrically. The image forming lens 26 isprovided in a movable manner via a driving mechanism (not shown) in aplane that includes the optical axis of the light deflected by the thirdmirror 24. The image forming lens 26 itself moves, thereby forming animage from the reflected light at a desired magnification. Then, in the4-line CCD sensor 1, the individual line sensors R, G, B, BW convertphotoelectrically the light coming in via the image forming lens 26pixel by pixel and output the resulting signals to the control unit 32.

[0045] Next, the configuration of the control system of the imagereading apparatus 10 will be explained.

[0046]FIG. 3 is a schematic block diagram of the control system of theimage reading apparatus 10.

[0047] On the control board 32 of the image reading apparatus 10, thereare provided a CPU 40, a ROM 41, a RAM 42, a signal processing section43, and a driving control section 44. The CPU 40 controls the entireimage reading apparatus 40. The ROM 41 is a memory in which controlprograms for performing the image reading operation and others arestored. The RAM 42 is a memory which stores data temporarily. The signalprocessing section 43 processes the signal from the 4-line CCD sensor 1and outputs the resulting signal to the outside world. The drivingcontrol section 44 has a motor driver which drives the driving motor 30.

[0048] The signal processing section 43 has a pre-processing circuit 51,a shading correction circuit 52, a line-to-line correction circuit 53,and an image processing circuit 54.

[0049] The preprocessing circuit 51 carries out processes, including anA/D conversion process of converting the analog signal from the 4-lineCCD sensor into a digital signal.

[0050] The shading correction circuit 52 makes correction in pixels onthe basis of the result of the reading of the shading correction plate11 by the 4-line CCD sensor 1. Specifically, the shading correctioncircuit 52 creates correction data for each pixel on the basis of theresult of the reading of the shading correction plate 11 as a whitereference plate by the 4-line CCD sensor 1. Furthermore, the shadingcorrection circuit 52 corrects the output signals from the individualline sensors R, G, B, BW of the 4-line CCD sensor 1 according to thecorrection data created on the basis of the result of the reading of theshading correction plate 11.

[0051] For example, on the basis of the black reference data previouslyread by the line sensors R, G, B, BW (the output signals from therespective line sensors when the exposure lamp 14 is off) and the whitereference data read from the shading correction plate 11 by the linesensors R, G, B, BW (the output signals from the respective line sensorswhen the shading correction plate 11 as a white reference plate is read)the shading correction circuit 52 corrects the output signals from theline sensors R, G, B, BW in pixels in reading the document image byusing the following equation:

I=K×(S−B)/(W−B)

[0052] where I is the signal after correction, K is a coefficient, S isthe output signal before correction (the output signal from the linesensor), B is the black reference data, and W is the white referencedata.

[0053] The line-to-line correction circuit 53 aligns the data from thered line sensor R, the data from the green line sensor G, and the datafrom the blue line sensor B with one another. Specifically, the red,green, and blue line sensors are so arranged that their lines areshifted several pixels from one another. For this reason, to create acolor image, the phases of the data from the line sensors R, G, and Bhave to be aligned with one another according to the movement speed inthe feed direction.

[0054] For example, in the configuration of FIG. 1, the red, green, andblue line sensors R, G, and B as color line sensors are arranged in thisorder: R, G, B, or in the order of scanning. The red line sensor R andthe green line sensor G are so arranged that they are spaced eightpixels apart. The green line sensor G and the blue line sensor B are soarranged that they are spaced eight pixels apart. In this case, if themagnification ratio is 25% to 400%, a positional correction of 2 to 32lines has to be made between R and G and between G and B in the datafrom the line sensors R, G, B.

[0055] For example, when the blue line sensor B is used as a reference,the line-to-line correction circuit 53 makes a positional adjustment of4 to 64 lines to the data from the red line sensor R and a positionaladjustment of 2 to 32 to the data from the green line sensor G. Makingsuch positional adjustments, the line-to-line correction circuit 53superimposes the data of the R signal, G signal, and B signal andcreates a color image with no off-shade part.

[0056] The image processing circuit 54 carries out an image process andoutputs the resulting image to the outside world. For example, whenoutputting a color image, the image processing circuit 54 makes a colorcorrection of the data subjected to the line-to-line correction andoutputs the resulting data to the outside world. When outputting amonochromatic image, the image processing circuit 54 effects thefiltering of the data of the BW signal passed through the line-to-linecorrection circuit and outputs the resulting data to the outside world.

[0057] To the CPU 40, an operation section 60 is connected. The user'soperation instruction is inputted to the operation section 60. Theoperation section 60 is provided with, for example, a setting key forsetting a read magnification, an image select key for selecting eithercolor or monochrome, a specify key for specifying the start of reading.For example, when the user specifies the reading mode for the documentfrom the operation section 60 and presses the key for specifying thestart of reading, the CPU 40 starts to read the document image accordingto the specified reading mode.

[0058] Furthermore, to the CPU 40, a switching circuit 61 and aswitching circuit 62 are connected. The switching circuit 61 is acircuit which switches between the G signal from the green line sensor Gand the BW signal from the black-and-white line sensor BW among thesignals supplied from the 4-line CCD sensor 1 to the signal processingsection 43. The switching circuit 62 is a circuit which switches betweenthe B signal from the blue sensor B and the BW signal from theblack-and-white line sensor BW among the signals supplied from the4-line CCD sensor 1 to the signal processing section 43.

[0059] Specifically, in the reading mode of reading images in color(color reading mode), the CPU 40 makes the G signal effective with theswitching circuit 61 and the B signal effective with the switchingcircuit 62. In this case, the 4-line CCD sensor 1 supplies the R signalfrom the red line sensor R, the G signal from the green line sensor G,and the B signal from the blue line sensor B to the signal processingsection 43. This enables the 4-line CCD sensor 1 to read a color image.

[0060] Furthermore, in the reading mode of reading images in monochrome(monochromatic reading mode), the CPU 40 makes not only the BW signaleffective with the switching circuit 61 but also the BW signal effectivewith the switching circuit 62. In this case, the 4-line CCD sensor 1supplies the BW signal from the black-and-white line sensor BW to thesignal processing section 43. This enables the 4-line CCD sensor 1 toread a monochromatic image.

[0061] With the configuration of FIG. 3, when reading a monochromaticimage, the 4-line CCD sensor 1 supplies the BW signals of the twochannels to the signal processing section 43. In this case, one channelsupplies the BW signal for an even number of lines and the othersupplies the BW signals for an odd number of lines.

[0062] Next, the operation of the image reading apparatus 1 will beexplained briefly.

[0063]FIG. 4 is a flowchart to help explain the read operation of theimage reading apparatus 10.

[0064] When the power key (not shown) is pressed, the CPU 40 executes aninitialize operation (step S11). In the initialize operation, the CPU 40carries out the initial operation of the entire image reading apparatus10, including the initialization of the driving reference point and thesetting of the amplification factor by the signal amplifying section.

[0065] After the initialize operation is completed, the CPU 40 bringsthe image reading apparatus 10 into the READY state of the image readingoperation (step S12). In this state, the user specified the imagereading mode from the operation section 60 and presses the start key forspecifying the start of image reading. At this time, the user chooseswhether the document image should be read in color (color reading mode)or in monochrome (monochromatic reading mode). After the user specifiesthe start of reading, the operation section 60 supplies not only asignal to request the start of document image reading but alsoinformation representing the document reading mode to the CPU 40.

[0066] Receiving the reading start request from the operation section60, the CPU 40 chooses either the color reading mode or themonochromatic reading mode, on the basis of the information representingthe reading mode from the operation section 60 (step S13).

[0067] When the color reading mode is chosen, the CPU 40 sets acolor-reading-mode operation according to the reading mode specified bythe user, such as a reading magnification (step S14). In the colorreading mode operation setting, for example, the reading position of theshading correction plate 11 and the reading position of the documentimage are set for the three line sensors R, G, B.

[0068] After the color reading mode operation setting is completed, theCPU 40 starts to move the first carriage 18. Then, the first carriage 18accelerates to the travel speed for reading set in the operationsetting. At the reading speed, the first carriage 18 moves in the feeddirection under the shading correction plate 11 and document table 12.When the first carriage 18 has arrived at under the shading correctionplate 11, the CPU 40 reads the shading correction plate 11 with thethree line sensors R, G, B acting as the color line sensors (step S15).The reading of the shading correction plate 11 by the color line sensorswill be explained in detail later.

[0069] When the first carriage 18 passes under the shading correctionplate 11 and arrives at the document image reading position, the CPU 40starts to read the image of the document placed on the document table 12by means of the three line sensors R, G, B acting as the color linesensors. Moreover, when the first carriage 18 has reached the readingend position of the document, the CPU 40 ends the reading of thedocument image (step S16).

[0070] After the document image has been read, the CPU 40 moves thefirst carriage 18 to a specific standby position. When the firstcarriage 18 has moved to the standby position, the CPU 40 returnscontrol to step S12 and brings the image reading apparatus 10 into theREADY state.

[0071] When the monochromatic reading mode is chosen in step S13, theCPU 40 sets a monochromatic-reading-mode operation according to thereading mode specified by the user, such as a reading magnification(step S17). In the monochromatic reading mode operation setting, forexample, the reading position of the shading correction plate 11 and thereading position of the document image are set for the monochromaticline sensor (black-and-white line sensor) BW.

[0072] After the monochromatic reading mode operation setting iscompleted, the CPU 40 starts to move the first carriage 18. Then, thefirst carriage 18 accelerates to the travel speed for reading set in theoperation setting. At the reading speed, the first carriage 18 moves inthe feed direction under the shading correction plate 11 and documenttable 12. When the first carriage 18 has arrived at under the shadingcorrection plate 11, the CPU 40 reads the shading correction plate 11with the black-and-white line sensor BW acting as the monochromatic linesensor (step S18). The reading of the shading correction plate 11 by themonochromatic line sensor will be explained in detail later.

[0073] When the first carriage 18 passes under the shading correctionplate 11 and arrives at the document image reading position, the CPU 40starts to read the image of the document placed on the document table 12by means of the black-and-white line sensor BW acting as themonochromatic line sensor. Moreover, when the first carriage 18 hasreached the reading end position of the document, the CPU 40 ends thereading of the document image (step S19). After the document image hasbeen read, the CPU 40 moves the first carriage 18 to a specific standbyposition. When the first carriage 18 has moved to the standby position,the CPU 40 returns control to step S12 and brings the image readingapparatus 10 into the READY state.

[0074] Next, the operation of reading the shading correction plate 11will be explained.

[0075] In shading correction explained below, suppose each of the linesensors R, G, B, BW of the 4-line CCD sensor 1 reads 16 lines of data asshading correction data.

[0076]FIG. 5 is a diagram to help explain the reading positions in acase where the line sensors R, G, B, BW read the shading correctionplate 11 in turn.

[0077] In the example of FIG. 5, it is assumed that the scanningpositions of the line sensors R, G, B, BW are arranged in the order ofBW, B, G, R in the direction in which the carriage 18 moves (or in thefeed direction) and that the control unit 32 takes in the signals fromthe 4-line CCD sensor in this order: the R signal, G signal, B signal,BW signal.

[0078] Specifically, in the example of FIG. 5, first, the red linesensor R reads the shading correction plate 11 by 16 lines. Then, thegreen line sensor G reads the shading correction plate 11 by 16 lines.Then, the blue line sensor B reads the shading correction plate 11 by 16lines. Then, the black-and-white line sensor BW reads the shadingcorrection plate 11 by 16 lines.

[0079] In this case, for example, if one line is 0.0425 mm in width(hereinafter, explanation will be given on the assumption that one lineis 0.0425 mm wide), the width needed for the red line sensor R to readthe shading correction plate 11 by 16 lines is 0.68 mm equivalent to 16lines.

[0080] Furthermore, the width needed for the green line sensor G to redthe shading correction plate 11 by 16 lines from the point where theread line sensor R read 16 lines is the sum of 0.34 mm equivalent to thespacing of 8 lines between the red line sensor R and the green linesensor G and 0.68 mm equivalent to 16 lines (the number of readinglines).

[0081] In addition, the width needed for the blue line sensor B to readthe shading correction plate 11 by 16 lines from the point where thegreen line sensor G read 16 lines is the sum of 0.34 mm equivalent tothe spacing of 8 lines between the green line sensor G and the blue linesensor B and 0.68 mm equivalent to 16 lines (the number of readinglines).

[0082] Moreover, the width needed for the black-and-white line sensor BWto read the shading correction plate 11 by 16 lines from the point wherethe blue line sensor B read 16 lines is the sum of 0.51 mm equivalent tothe spacing of 12 lines between the blue line sensor B and theblack-and-white line sensor BW and 0.68 mm equivalent to 16 lines (thenumber of reading lines).

[0083] Therefore, in the example of FIG. 5, the width in the feeddirection of the shading correction plate 11 has to be equal to at leastthe total (3.91 mm equivalent to 92 lines) of the reading widths(equivalent to 16×4 lines) of the four line sensors R, G, B. BW and thetotal spacing between the four line sensors (equivalent to 8×2+12lines). In FIG. 5, during the time from when the reading of the shadingcorrection plate 11 is started until the reading is completed, the firstcarriage 18 requires a travel distance L0 of 2.72 mm equivalent to 64(16×4) lines.

[0084] Hereinafter, a first to a third reading method for the shadingcorrection method 11 will be explained.

[0085] The first to third reading methods can be applied to the imagereading apparatus 10 where the scanning positions of the line sensors R,G, B, BW are arranged in the order of R, G, B, BW in the direction inwhich the first carriage 18 moves (or in the feed direction).

[0086] First, the first reading method for the shading correction plate11 will be explained.

[0087]FIG. 6 is a diagram to help explain the first reading method forthe shading correction plate 11. In the example of FIG. 6, the scanningpositions of the line sensors R, G, B, BW are arranged in the order ofR, G, B, BW in the direction in which the first carriage 18 moves (or inthe feed direction). In FIG. 6, suppose, in the color reading mode, thecontrol unit 32 reads the signals from the three line sensors R, G, B inthis order: the B signal, the G signal, and the R signal.

[0088] In FIG. 6, in the color reading mode, with the scanning positionof the blue line sensor B as the reading start position (the trailingedge in the feed direction of the shading correction plate 11), the blueline sensor B first reads the shading correction plate 11 by 16 lines.Then, the green line sensor G reads the shading correction plate 11 by16 lines. Thereafter, the red line sensor R reads the shading correctionplate 11 by 16 lines.

[0089] Specifically, in the color reading mode, the width in the feeddirection of the shading correction plate 11 is equal to the total (2.72mm) of the width (0.68 mm) needed for the blue line sensor B to read 16lines, the spacing of 8 lines (0.34 mm) between the blue line sensor Band the green line sensor G, the width (0.68 mm) needed for the greenline sensor G to read 16 lines, the spacing of 8 lines (0.34 mm) betweenthe green line sensor G and the red line sensor R, and the width (0.68mm) needed for the red line sensor R to read 16 lines. In addition, whenthe shading correction plate 11 is read in the color reading mode, thetravel distance L11 of the first carriage 18 is equivalent to 48 lines(16×3 lines).

[0090] In the monochromatic reading mode, with the scanning position ofthe black-and-white line sensor BW as the reading start position (thetrailing edge in the feed direction of the shading correction plate 11),the black-and-white line sensor BW reads the shading correction plate 11by 16 lines. Specifically, in the monochromatic reading mode, the widthin the feed direction needed for the black-and-white line sensor BW toread the shading correction plate 11 by 16 lines is 0.68 mm equivalentto 16 lines (the number of reading lines). In addition, when the shadingcorrection plate 11 is read in the monochromatic reading mode, thetravel distance L21 of the first carriage 18 is equivalent to 16 lines.

[0091] As described above, in the first reading method, the width in thefeed direction of the shading correction plate 11 has to be equal to thetotal (equivalent to 64 lines) of the reading widths (equivalent to 16×3lines) of at least the three line sensors R, G, and B and the totalspacing (equivalent to 8×2 lines) between the three line sensors in thecolor reading mode. In the monochromatic reading mode, the width has tobe the reading width (equivalent to 16 lines) of at least theblack-and-white line sensor BW.

[0092] Furthermore, in the first embodiment, the reading start positionof the shading correction plate 11 in the monochromatic reading mode andthe reading start position of the shading correction plate 11 in thecolor reading mode are set separately.

[0093] Therefore, in the first reading method of FIG. 6, the shadingcorrection plate 11 has only to have a width of 64 lines in the feeddirection. Specifically, as compared with the reading method of FIG. 5,in the first method, the width in the feed direction of the shadingcorrection plate 11 can be decreased by the total of the spacing(equivalent to 12 lines) between the color line sensors (three linesensors R, G, B) and the monochromatic line sensor (black-and-white linesensor BW) and the reading width (equivalent to 16 lines) of theblack-and-white line sensor BW. In addition, the travel distance of thefirst carriage in reading the shading correction plate can be decreasedby the travel distance (equivalent to 16 lines) needed to read theblack-and-white line sensor BW. This is the effect obtained because thereading position (the reading start position) of the shading correctionplate in the color reading mode and the reading position (the readingstart position) of the shading correction plate in the monochromaticreading mode have been set in separate positions.

[0094] Next, the second reading method for the shading correction plate11 will be explained.

[0095]FIG. 7 is a diagram to help explain the second reading method forthe shading correction plate 11. In the example of FIG. 7, the scanningpositions of the line sensors R, G, B, BW are arranged in the order ofR, G, B, BW in the direction in which the first carriage 18 moves (or inthe feed direction). In FIG. 7, suppose, in the color reading mode, thecontrol unit 32 reads the signals from the three line sensors R, G, B inthis order: the R signal, the G signal, and the B signal.

[0096] In FIG. 7, in the color reading mode, with the scanning positionof the red line sensor R as the reading start position (the trailingedge in the feed direction of the shading correction plate 11), the redline sensor R first reads the shading correction plate 11 by 16 lines.Then, the green line sensor G reads the shading correction plate 11 by16 lines. Thereafter, the blue line sensor B reads the shadingcorrection plate 11 by 16 lines.

[0097] Specifically, in the color reading mode, the width in the feeddirection of the shading correction plate is equal to the total (1.36mm) of the width (0.38 mm) obtained by subtracting the spacing of 8lines (0.34 mm) between the red line sensor R and the green line sensorG from the width (0.68 mm) needed for the red line sensor R to read 16lines, the width (0.38 mm) obtained by subtracting the spacing of 8lines (0.34 mm) between the green line sensor G and the blue line sensorB from the width (0.68 mm) needed for the green line sensor G to read 16lines, and the width (0.68 mm) needed for the blue line sensor B to read16 lines. In addition, when the shading correction plate 11 is read inthe color reading mode, the travel distance L12 of the first carriage 18is equivalent to 48 lines (16×3 lines) as is the travel distance L11 inthe first reading method.

[0098] In the monochromatic reading mode, with the scanning position ofthe black-and-white line sensor BW as the reading start position (thetrailing edge in the feed direction of the shading correction plate 11),the black-and-white line sensor BW reads the shading correction plate 11by 16 lines. Specifically, in the monochromatic reading mode, the widthin the feed direction needed for the black-and-white line sensor BW toread the shading correction plate 11 by 16 lines is 0.68 mm equivalentto 16 lines (the number of reading lines). In addition, when the shadingcorrection plate 11 is read in the monochromatic reading mode, thetravel distance L22 of the first carriage 18 is equivalent to 16 linesas is the travel distance L21 in the first reading method.

[0099] As described above, in the second embodiment, the reading startposition of the shading correction plate 11 in the color reading modeand the reading start position of the shading correction plate 11 in themonochromatic reading mode are set separately. The width in the feeddirection of the shading correction plate 11 has to be equal to thevalue (equivalent to 32 lines) obtained by subtracting the total spacingbetween the three line sensors (equivalent to 8×2 lines) from thereading widths of at least the three line sensors R, G, and B(equivalent to 16×3 lines) in the color reading mode. In themonochromatic reading mode, the width has to be the reading width(equivalent to 16 lines) of at least the black-and-white line sensor BW.

[0100] Therefore, in the second reading method of FIG. 7, the shadingcorrection plate has only to have a width of 32 lines in the feeddirection. Specifically, in the second reading method of FIG. 7, thetravel distance of the first carriage in reading the shading correctionplate is the same as in the first reading method of FIG. 6 and the widthin the feed direction of the shading correction plate is decreased bytwice the total spacing between the three line sensors.

[0101] Next, the third reading method for the shading correction plate11 will be explained.

[0102]FIG. 8 is a diagram to help explain the third reading method forthe shading correction plate 11. In the example of FIG. 8, the scanningpositions of the line sensors R, G, B, BW are arranged in the order ofR, G, B, BW in the direction in which the first carriage 18 moves (or inthe feed direction). In FIG. 8, suppose, in the color reading mode, thecontrol unit 32 takes in the signals (the R signal, G signal, and Bsignal) from the three line sensors R, G, B at the same time.

[0103] In FIG. 8, in the color reading mode, with the scanning positionof the blue line sensor B as the reading start position (the trailingedge in the feed direction of the shading correction plate 11), the redline sensor R, green line sensor G, and blue line sensor B each read theshading correction plate 11 by 16 lines at the same time.

[0104] Specifically, in the color reading mode, the width in the feeddirection of the shading correction plate 11 is equal to the total (1.36mm) of the width (0.68 mm) required for each of the red line sensor R,green line sensor G, and blue line sensor B to read 16 lines, thespacing (0.34 mm) of 8 lines between the red line sensor R and the greenline sensor G, and the spacing (0.34 mm) of 8 lines between the greenline sensor G and the blue line sensor B. In addition, when the shadingcorrection plate 11 is read in the color reading mode, the traveldistance L13 of the first carriage 18 is equivalent to 16 lines.

[0105] In the monochromatic reading mode, with the scanning position ofthe black-and-white line sensor BW as the reading start position (thetrailing edge in the feed direction of the shading correction plate 11),the black-and-white line sensor BW reads the shading correction plate 11by 16 lines. Specifically, in the monochromatic reading mode, the widthin the feed direction needed for the black-and-white line sensor BW toread the shading correction plate 11 by 16 lines is 0.68 mm equivalentto 16 lines (the number of reading lines). In addition, when the shadingcorrection plate 11 is read in the monochromatic reading mode, thetravel distance L23 of the first carriage 18 is equivalent to 16 lines.

[0106] As described above, in the third reading method, the readingstart position of the shading correction plate 11 in the color readingmode and the reading start position of the shading correction plate 11in the monochromatic reading mode are set separately. The width in thefeed direction of the shading correction plate 11 has to be equal to thetotal (equivalent to 32 lines) of the reading widths (equivalent to 16lines) of the line sensors R, G, B and the total spacing between thethree line sensors (equivalent to 8×2 lines) in the color reading mode.In the monochromatic reading mode, the width has to be the reading width(equivalent to 16 lines) of at least the black-and-white line sensor BW.

[0107] Therefore, in the third reading method of FIG. 8, the shadingcorrection plate has only to have a width of 32 lines in the feeddirection. Specifically, in the third reading method of FIG. 8, thewidth in the feed direction of the shading correction plate is the sameas in the second reading method of FIG. 7, but the travel distance ofthe first carriage in reading the shading correction plate can be madesmaller. If the travel speed of the first carriage in the third readingmethod is the same as that in the second reading method, the timerequired to read the shading correction plate can be made shorter in thethird reading method than in the second reading method. Therefore, thetime needed to make a shading correction can be made shorter.

[0108] Hereinafter, a fourth to a sixth reading method for the shadingcorrection method 11 will be explained.

[0109] The fourth to sixth reading methods can be applied to the imagereading apparatus 10 where the scanning positions of the line sensors R,G, B, BW are arranged in the order of BW, B, G, R in the direction inwhich the first carriage 18 moves (or in the feed direction).

[0110] First, the fourth reading method for the shading correction plate11 will be explained.

[0111]FIG. 9 is a diagram to help explain the fourth reading method forthe shading correction plate 11. In the example of FIG. 9, the scanningpositions of the line sensors R, G, B, BW are arranged in the order ofBW, B, G, R in the direction in which the first carriage 18 moves (or inthe feed direction). In FIG. 9, suppose, in the color reading mode, thecontrol unit 32 reads the signals from the three line sensors R, G, B inthis order: the R signal, the G signal, and the B signal.

[0112] In FIG. 9, in the color reading mode, with the scanning positionof the red line sensor R as the reading start position (the trailingedge in the feed direction of the shading correction plate 11), the redline sensor R first reads the shading correction plate 11 by 16 lines.Then, the green line sensor G reads the shading correction plate 11 by16 lines. Thereafter, the blue line sensor B reads the shadingcorrection plate 11 by 16 lines.

[0113] Specifically, in the color reading mode, the width in the feeddirection of the shading correction plate 11 is equal to the total (2.72mm) of the width (0.68 mm) needed for the red line sensor R to read 16lines, the spacing of 8 lines (0.34 mm) between the red line sensor Rand the green line sensor G, the width (0.68 mm) needed for the greenline sensor G to read 16 lines, the spacing of 8 lines (0.34 mm) betweenthe green line sensor G and the blue line sensor B, and the width (0.68mm) needed for the blue line sensor B to read 16 lines. In addition,when the shading correction plate 11 is read in the color reading mode,the travel distance L14 of the first carriage 18 is equivalent to 48lines (16×3 lines).

[0114] In the monochromatic reading mode, with the scanning position ofthe black-and-white line sensor BW as the reading start position (thetrailing edge in the feed direction of the shading correction plate 11),the black-and-white line sensor BW reads the shading correction plate 11by 16 lines. Specifically, in the monochromatic reading mode, the widthin the feed direction needed for the black-and-white line sensor BW toread the shading correction plate 11 by 16 lines is 0.68 mm equivalentto 16 lines (the number of reading lines). In addition, when the shadingcorrection plate 11 is read in the monochromatic reading mode, thetravel distance L24 of the first carriage 18 is equivalent to 16 lines.

[0115] As described above, in the fourth reading method, the readingstart position of the shading correction plate 11 in the color readingmode and the reading start position of the shading correction plate 11in the monochromatic reading mode are set separately as in the firstreading method. The width in the feed direction of the shadingcorrection plate 11 has to be equal to the total (equivalent to 64lines) of the reading widths (equivalent to 16×3 lines) of at least thethree line sensors R, G, and B and the total spacing between the threeline sensors (equivalent to 8×2 lines) in the color reading mode. In themonochromatic reading mode, the width has to be the reading width(equivalent to 16 lines) of at least the black-and-white line sensor BW.

[0116] Therefore, in the fourth reading method of FIG. 9, the shadingcorrection plate has only to have a width of 64 lines in the feeddirection. Specifically, as compared with the reading method of readingthe four line sensors R. G, B, BW in the order of R, G, B, BW, in thefourth reading method, the width in the feed direction of the shadingcorrection plate 11 can be decreased by the total of the spacing (12lines) between the color line sensors (three line sensors R, G, B) andthe monochromatic line sensor (black-and-white line sensor BW) and thereading width (equivalent to 16 lines) of the black-and-white linesensor BW. In addition, the travel distance of the first carriage inreading the shading correction plate can be decreased by the traveldistance (equivalent to 16 lines) needed for the black-and-white linesensor BW to read. This is the effect obtained because the readingposition (the reading start position) of the shading correction plate inthe color reading mode and the reading position (the reading startposition) of the shading correction plate in the monochromatic readingmode have been set in separate positions.

[0117] Next, the fifth reading method for the shading correction plate11 will be explained.

[0118]FIG. 10 is a diagram to help explain the fifth reading method forthe shading correction plate 11. In the example of FIG. 10, the scanningpositions of the line sensors R, G, B, BW are arranged in the order ofBW, B, G, R in the direction in which the first carriage 18 moves (or inthe feed direction). In FIG. 10, suppose, in the color reading mode, thecontrol unit 32 reads the signals from the three line sensors R, G, B inthis order: the B signal, the G signal, and the R signal.

[0119] In FIG. 10, in the color reading mode, with the scanning positionof the blue line sensor B as the reading start position (the trailingedge in the feed direction of the shading correction plate 11), the blueline sensor B first reads the shading correction plate 11 by 16 lines.Then, the green line sensor G reads the shading correction plate 11 by16 lines. Thereafter, the red line sensor R reads the shading correctionplate 11 by 16 lines.

[0120] Specifically, in the color reading mode, the width in the feeddirection of the shading correction plate 11 is equal to the total (1.36mm) of the width (0.38 mm) obtained by subtracting the spacing of 8lines (0.34 mm) between the blue line sensor B and the green line sensorG from the width (0.68 mm) needed for the blue line sensor R to read 16lines, the width (0.38 mm) obtained by subtracting the spacing of 8lines (0.34 mm) between the green line sensor G and the red line sensorR from the width (0.68 mm) needed for the green line sensor G to read 16lines, and the width (0.68 mm) needed for the red line sensor R to read16 lines. In addition, when the shading correction plate 11 is read inthe color reading mode, the travel distance L15 of the first carriage 18is equivalent to 48 lines (16×3 lines) as is the travel distance L14 inthe fourth reading method.

[0121] In the monochromatic reading mode, with the scanning position ofthe black-and-white line sensor BW as the reading start position (thetrailing edge in the feed direction of the shading correction plate 11),the black-and-white line sensor BW reads the shading correction plate 11by 16 lines. Specifically, in the monochromatic reading mode, the widthin the feed direction needed for the black-and-white line sensor BW toread the shading correction plate 11 by 16 lines is 0.68 mm equivalentto 16 lines (the number of reading lines). In addition, when the shadingcorrection plate 11 is read in the monochromatic reading mode, thetravel distance L25 of the first carriage 18 is equivalent to 16 linesas is the travel distance L24 in the fourth reading method.

[0122] As described above, in the fifth embodiment, the reading startposition of the shading correction plate 11 in the color reading modeand the reading start position of the shading correction plate 11 in themonochromatic reading mode are set separately. The width in the feeddirection of the shading correction plate 11 has to be equal to thevalue (equivalent to 32 lines) obtained by subtracting the total spacingbetween the three line sensors (equivalent to 8×2 lines) from thereading widths of at least the three line sensors R, G, and B(equivalent to 16×3 lines) in the color reading mode. In themonochromatic reading mode, the width has to be the reading width(equivalent to 16 lines) of at least the black-and-white line sensor BW.

[0123] Therefore, in the fifth reading method of FIG. 10, the shadingcorrection plate has only to have a width of 32 lines in the feeddirection. Specifically, in the fifth reading method of FIG. 10, thetravel distance of the first carriage in reading the shading correctionplate is the same as in the fourth reading method of FIG. 9 and thewidth in the feed direction of the shading correction plate is decreasedby twice the total spacing between the three line sensors.

[0124] Next, the sixth reading method for the shading correction plate11 will be explained.

[0125]FIG. 11 is a diagram to help explain the sixth reading method forthe shading correction plate 11. In the example of FIG. 11, the scanningpositions of the line sensors R, G, B, BW are arranged in the order ofBW, B, G, R in the direction in which the first carriage 18 moves (or inthe feed direction). In FIG. 11, suppose, in the color reading mode, thecontrol unit 32 takes in the signals (the R signal, G signal, and Bsignal) from the three line sensors R, G, B at the same time.

[0126] In FIG. 11, in the color reading mode, with the scanning positionof the red line sensor R as the reading start position (the trailingedge in the feed direction of the shading correction plate 11), the redline sensor R, green line sensor G, and blue line sensor B each read theshading correction plate 11 by 16 lines at the same time.

[0127] Specifically, in the color reading mode, the width in the feeddirection of the shading correction plate 11 is equal to the total (1.36mm) of the width (0.68 mm) required for each of the red line sensor R,green line sensor G, and blue line sensor B to read 16 lines, thespacing (0.34 mm) of 8 lines between the red line sensor R and the greenline sensor G, and the spacing (0.34 mm) of 8 lines between the greenline sensor G and the blue line sensor B. In addition, when the shadingcorrection plate 11 is read in the color reading mode, the traveldistance L16 of the first carriage 18 is equivalent to 16 lines.

[0128] In the monochromatic reading mode, with the scanning position ofthe black-and-white line sensor BW as the reading start position (thetrailing edge in the feed direction of the shading correction plate 11),the black-and-white line sensor BW reads the shading correction plate 11by 16 lines. Specifically, in the monochromatic reading mode, the widthin the feed direction needed for the black-and-white line sensor BW toread the shading correction plate 11 by 16 lines is 0.68 mm equivalentto 16 lines (the number of reading lines). In addition, when the shadingcorrection plate 11 is read in the monochromatic reading mode, thetravel distance L26 of the first carriage 18 is equivalent to 16 lines.

[0129] As described above, in the sixth reading method, the readingstart position of the shading correction plate 11 in the color readingmode and the reading start position of the shading correction plate 11in the monochromatic reading mode are set separately. The width in thefeed direction of the shading correction plate 11 has to be equal to thetotal (equivalent to 32 lines) of the reading widths (equivalent to 16lines) of the line sensors R, G, B and the total spacing between thethree line sensors (equivalent to 8×2 lines) in the color reading mode.In the monochromatic reading mode, the width has to be the reading width(equivalent to 16 lines) of at least the black-and-white line sensor BW.

[0130] Therefore, in the sixth reading method of FIG. 11, the shadingcorrection plate has only to have a width of 32 lines in the feeddirection. Specifically, in the sixth reading method of FIG. 11, thewidth in the feed direction of the shading correction plate is the sameas in the fifth reading method of FIG. 10, but the travel distance ofthe first carriage in reading the shading correction plate can be madesmaller. If the travel speed of the first carriage in the sixth readingmethod is the same as that in the fifth reading method, the timerequired to read the shading correction plate can be made shorter in thesixth reading method than in the fifth reading method. Therefore, thetime needed to make a shading correction can be made shorter.

[0131] Next, the difference between the first to sixth reading methodsand their applications will be explained.

[0132] The first to sixth reading methods are selected suitablyaccording to the specifications of the image reading apparatus,including the arrangement of the scanning positions of the line sensorsin the feed direction, the order in which the signals from the sensorsare taken in, and the way the signals from the sensors are taken in.This makes it possible to design the best shading correction plate andmake the most suitable shading correction according to various types ofimage reading apparatuses.

[0133] The first to third reading methods are applied to, for example,the following image reading apparatuses.

[0134] The first reading method can be applied to an image readingapparatus where the arrangement of the scanning positions in the feeddirection of the line sensors R, G, B, BW in the 4-line CCD sensor 1 isin the order of R, G, B, BW and the color line sensors R, G, B aredesigned to read the shading correction plate 11 in this order: B, G, R.

[0135] The second reading method can be applied to an image readingapparatus where the arrangement of the scanning positions in the feeddirection of the line sensors R, G, B, BW in the 4-line CCD sensor 1 isin the order of R, G, B, BW and the color line sensors R, G, B aredesigned to read the shading correction plate 11 in this order: R, G, B.

[0136] When the arrangement of the scanning positions in the feeddirection of the line sensors R, G, B, BW in the 4-line CCD sensor 1 isin the order of R, G, B, BW and the order in which the color linesensors R, G, B reads can be selected, the first or second readingmethod can be applied. Since the shading correction plate 11 can be madenarrower in the second reading method than in the first reading method,it is desirable to apply the second reading method.

[0137] The third reading method can be applied to an image readingapparatus where the arrangement of the scanning positions in the feeddirection of the line sensors R, G, B, BW in the 4-line CCD sensor 1 isin the order of R, G, B, BW and the color line sensors R, G, B aredesigned to read the shading correction plate 11 at the same time.

[0138] The fourth to sixth reading methods are applied to, for example,the following image reading apparatuses.

[0139] The fourth reading method can be applied to an image readingapparatus where the arrangement of the scanning positions in the feeddirection of the line sensors R, G, B, BW in the 4-line CCD sensor 1 isin the order of BW, B, G, R and the color line sensors R, G, B aredesigned to read the shading correction plate 11 in this order: R, G, B.

[0140] The fifth reading method can be applied to an image readingapparatus where the arrangement of the scanning positions in the feeddirection of the line sensors R, G, B, BW in the 4-line CCD sensor 1 isin the order of BW, B, G, R and the color line sensors R, G, B aredesigned to read the shading correction plate 11 in this order: B, G, R.

[0141] When the arrangement of the scanning positions in the feeddirection of the line sensors R, G, B, BW in the 4-line CCD sensor 1 isin the order of BW, B, G, R and the order in which the color linesensors R, G, B reads can be selected, the fourth or fifth readingmethod can be applied. Since the shading correction plate 11 can be madenarrower in the fifth reading method than in the fourth reading method,it is desirable to apply the fifth reading method.

[0142] The sixth reading method can be applied to an image readingapparatus where the arrangement of the scanning positions in the feeddirection of the line sensors R, G, B, BW in the 4-line CCD sensor 1 isin the order of BW, B, G, R and the color line sensors R, G, B aredesigned to read the shading correction plate 11 at the same time.

[0143] In the embodiment, as explained in the first to sixth readingmethod, in the image reading apparatus having the color line sensors andthe monochromatic line sensor different from the color line sensors, thereading position of the shading correction plate in the color readingmode and the reading position of the shading correction plate in themonochromatic reading mode are set independently. This makes it possibleto make narrower the width in the feed direction of the shadingcorrection plate.

[0144] From the viewpoint of carriage driving control, when the readingof the shading correction plate is started at the same position in boththe color reading mode and the monochromatic reading mode, this makesthe driving distance longer in reading the shading correction plate. Incontrast, setting the reading start position in the color reading modeand that in the monochromatic reading mode to the optimum positionsseparately makes it possible to shorten the travel distance in readingthe shading correction plate and read the shading correction plateefficiently.

[0145] As described above in detail, with the above-described imagereading method, the width of the reference plate can be narrower and theshading correction can be made efficiently even in an image readingapparatus which reads images with a line sensor having color linesensors and a monochromatic line sensor. Consequently, use of the imagereading method enables the image reading apparatus to be made smallerand more stable.

[0146] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiment shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. An image reading apparatus which reads images onthe reading face of a document in color or in monochrome, the imagereading apparatus comprising: a line sensor which includes a color linesensor for reading a color image and a monochromatic line sensor forreading a monochromatic image different from the color line sensor; ascanning section on which an optical system for directing light from thereading face of the document to the line sensor is provided; a drivingmechanism which moves the scanning section in a feed direction withrespect to the reading face of the document; a reference plate which isprovided in front of the leading edge of the reading face of thedocument in the feed direction in which the scanning section is moved bythe driving mechanism; and a control section which, when the readingface of the document is read in color, starts to read the referenceplate with the color line sensor at the time that the scanning sectionmoved in the feed direction by the driving mechanism reaches a colorreading start position for the reference plate, thereby reading thereference plate with the color line sensor, and which, when the readingface of the document is read in monochrome, starts to read the referenceplate with the monochromatic line sensor at the time that the scanningsection moved in the feed direction by the driving mechanism reaches amonochromatic reading start position for the reference plate, therebyreading the reference plate with the monochromatic line sensor.
 2. Theimage reading apparatus according to claim 1, wherein the controlsection, when the reading face of the document is read in color, causesthe driving mechanism to move the scanning section in the feed directionand starts to read the reference plate with the color line sensor at thetime that the scanning section reaches the color reading start positionfor the reference plate, thereby reading the reference plate with thecolor line sensor, and further corrects the data on the reading face ofthe document read by the color line sensor on the basis of the data onthe reference plate read by the color line sensor, and when the readingface of the document is read in monochrome, causes the driving mechanismto move the scanning section in the feed direction and starts to readthe reference plate with the monochromatic line sensor at the time thatthe scanning section reaches the monochromatic reading start positionfor the reference plate, thereby reading the reference plate with themonochromatic line sensor, and further corrects the data on the readingface of the document read by the monochromatic line sensor on the basisof the data on the reference plate read by the monochromatic linesensor.
 3. The image reading apparatus according to claim 1, wherein thecolor line sensor is composed of a plurality of line sensors whosescanning positions are arranged at specific intervals in the feeddirection, and the control section, when the reading face of thedocument is read in color, causes the driving mechanism to move thescanning section in the feed direction and causes the individual linesensors of the color line sensor to start to read the reference plate inturn at the time that the scanning position of the line sensor whosescanning position is at the rear in the color line sensor in the feeddirection reaches the reading start position for the reference plate,thereby reading the reference plate with the color line sensor.
 4. Theimage reading apparatus according to claim 1, wherein the color linesensor is composed of a plurality of line sensors whose scanningpositions are arranged at specific intervals in the feed direction, andthe control section, when the reading face of the document is read incolor, causes the driving mechanism to move the scanning section in thefeed direction and causes the individual line sensors of the color linesensor to start to read the reference plate in turn at the time that thescanning position of the line sensor whose scanning position is at thehead in the color line sensor in the feed direction reaches the readingstart position for the reference plate, thereby reading the referenceplate with the color line sensor.
 5. The image reading apparatusaccording to claim 1, wherein the color line sensor is composed of aplurality of line sensors whose scanning positions are arranged atspecific intervals in the feed direction, and the control section, whenthe reading face of the document is read in color, causes the drivingmechanism to move the scanning section in the feed direction and causesthe individual line sensors of the color line sensor to start to readthe reference plate at the same time at the time that the scanningposition of the line sensor whose scanning position is at the rear inthe color line sensor in the feed direction reaches the reading startposition for the reference plate, thereby reading the reference platewith the color line sensor.
 6. An image reading method used in an imagereading apparatus which comprises a line sensor which includes a colorline sensor for reading a color image and a monochromatic line sensorfor reading a mono-chromatic image different from the color line sensor,a scanning section on which an optical system for directing light fromthe reading face of the document to the line sensor is provided, adriving mechanism which moves the scanning section in a feed directionwith respect to the reading face of the document, and a reference platewhich is provided in front of the leading edge of the reading face ofthe document in the feed direction in which the scanning section ismoved by the driving mechanism, the image reading method comprising:when the reading face of the document is read in color, starting to readthe reference plate with the color line sensor at the time that thescanning section moved in the feed direction by the driving mechanismreaches a color reading start position for the reference plate andthereby reading the reference plate with the color line sensor; and whenthe reading face of the document is read in monochrome, starting to readthe reference plate with the monochromatic line sensor at the time thatthe scanning section moved in the feed direction by the drivingmechanism reaches a monochromatic reading start position for thereference plate and thereby reading the reference plate with themonochromatic line sensor.
 7. The image reading method according toclaim 6, further comprising: when the reading face of the document isread in color, reading the reference plate with the color line sensorand then correcting the data on the reading face of the document read bythe color line sensor on the basis of the data on the reference plateread by the color line sensor, and when the reading face of the documentis read in monochrome, reading the reference plate with themonochromatic line sensor and then correcting the data on the readingface of the document read by the monochromatic line sensor on the basisof the data on the reference plate read by the monochromatic linesensor.
 8. The image reading method according to claim 6, wherein thecolor line sensor is composed of a plurality of line sensors whosescanning positions are arranged at specific intervals in the feeddirection, and the act of reading the reference plate with the colorline sensor is to cause the driving mechanism to move the scanningsection in the feed direction and cause the individual line sensors ofthe color line sensor to start to read the reference plate in turn atthe time that the scanning position of the line sensor whose scanningposition is at the rear in the color line sensor in the feed directionreaches the reading start position for the reference plate, therebyreading the reference plate with the color line sensor.
 9. The imagereading method according to claim 6, wherein the color line sensor iscomposed of a plurality of line sensors whose scanning positions arearranged at specific intervals in the feed direction, and the act ofreading the reference plate with the color line sensor is to cause thedriving mechanism to move the scanning section in the feed direction andcause the individual line sensors of the color line sensor to start toread the reference plate in turn at the time that the scanning positionof the line sensor whose scanning position is at the head in the colorline sensor in the feed direction reaches the reading start position forthe reference plate, thereby reading the reference plate with the colorline sensor.
 10. The image reading method according to claim 6, whereinthe color line sensor is composed of a plurality of line sensors whosescanning positions are arranged at specific intervals in the feeddirection, and the act of reading the reference plate with the colorline sensor is to cause the driving mechanism to move the scanningsection in the feed direction and cause the individual line sensors ofthe color line sensor to start to read the reference plate at the sametime at the time that the scanning position of the line sensor whosescanning position is at the rear in the color line sensor in the feeddirection reaches the reading start position for the reference plate,thereby reading the reference plate with the color line sensor.